After check a mistake has been found on the magnification. This seems to be the good calibration (feel free to cross check). The projection of the 2mm hex is attached

the calibration are :

NF_Refl: acA1920-40gm
    pixel size (real): 5.86um
    Magnification = 1.71
    pixel size (image): 10um
    image donne on input plan mirror M1 (accuracy about few mm)

NF_Trans: acA1920-40gm
    pixel size (real): 5.86um
    Magnification = 0.68
    pixel size (image): 4um
    image donne on output plan mirror M2 (accuracy about few mm)

The NF_inj was calibrated with the USB microscope (1.4um/pixel on microscope image). The 5th ring of the lens is about 1.89 mm in diameter.

NF_inj: acA1920-40gm
    pixel size (real): 5.86um
    Magnification = 1.54
    pixel size (image): 9um

J'ai fait le calcul de la puissance du Tangor qui passait à travers le glan avec 3 hypothèses :

1- Le faisceau est totalement polarisé et le glan est parfait (cf : image 1)

2- Le faisceau est totalement polarisé et le glan est imparfait (cf : image 2)

3- Le faisceau est partiellement polarisé et le glan est imparfait (cf : image 3)

La quatrième image montre la cause du "bump" liée au stacking du Tangor sur la voie PDH.

Comme j'ai aligné le glan quand la cavité n'était pas lockée et que j'ai fait matché la polar avant la cavité avec celle du glan (toujours pas locké), dans le cas où la polar de la cavité lockée est différente (ici le cas critique est représenté), il y a une fraction du Tangor qui va passer à travers le cube.

Les trois premières images sont la premières injection d'un burst dans la cavité à 3 instant t. On remarque plusieurs choses :

- Le burst peut être plus ou moins bien injecté

- Il y a un "bump" sur la photodiode de la voie de réflexion (changement polar ??? ), qui atteint se valeur maximale quand le burst est injecté au mieux

- Il y a un offset sur le PDH qui varie, il est minimal quand le burst est bien injecté et augmente quand il est de moins en moins bien injecté (Une cause de la mauvaise injection du burst ??)

La quatrième image représente un délock/relock avec la lockline uniquement. Le signal sur la photodiode de réflexion n'est pas très élevé (désaligné? autre?)

Les trois dernières images représentent l'injection d'un burst au mieux possible après avoir changé la valeur de l'AOM lockline, ce qui a pour effet de jouer sur la CEP.

3 phase noise measurements made on the Amplitude GHz oscillator with different PZT configurations :

- black curve: PZT connector is open
- green curve: PZT connector is shorted by 50 ohms
- blue curve: PZT is excited by 100mVrms of white noise coming from a generator.

on the blue curve, one can clearly see a phase noise increase in the region 10kHz - 1MHz but it is not evident the peaks seen with the PZT open or shorted are related to the peaks excited with the noise injected on the PZT.

with a PZT not excited, one can just observe that the phase noise is decreasing a lot around 10kHz to reach the reference oscillator phase noise floor and then increase again exactly when the PZT resonant frequencies appear, between 20kHz and 200kHz.... reaching at the end the phase noise detection floor.

I add below the measurements done on October 20th, the ones done in September which are very similar and on which one can see a peak around 26kHz.

Thorlabs PZT datasheet.
Reference: PC4QR

Following the Helium Neon Alignment + change in the distance between the mirrors to be; M3-M4 = 90.5 mm , M1-M2 = 80.2 mm  -→ The alignment using the Koheras CW laser is done.

• Additional components used:
  • for monitoring beam :  Photodiode (power of beam), Beam Profiler (shape, position, power , ... ) 
  • for Koheras frequency scan: function generator, Amplifier or use lase-lock (had some issues to be checked)
  • Telescope: made using 1 m focal length to match the beam shape of the cavity
• Observed during:
  • The alignment is fairly similar to the previous one, placed two irises to preserve it.
  • Fundamental mode observed (beam profiler after M2) was circular
  • when the frequency scan was fine-tuned around the fundamental mode we could see the mode pulsing in the cavity, but there was a bit of instability.
  • when doing a very wide frequency scan (50 V ~ 1.5 GHz), multiple modes where showing inside the cavity

Photos attached show:

• some resonating modes in the cavity 
• Fundamental mode resonating in the cavity, with its properties (2D shape, 1D shape, position) ** The picture is taken after subtracting the background **
  • from 2D it is very circular
  • from 1D it is confirmed to be circular (715.00 um - 704.00 um)
  • From position, we have a reference to compare with tomorrow morning.
• Diffraction that can be observed in the cavity (you can clearly see the edges of the mirrors in the photo)
• The temperature curve is attached for the duration of the exp. (before starting Ronic switched something off and then put it on !!!!!! it seems to be for temp regulation )

** Notes for tomorrow morning :  first : switch on the laser and check if the beam 00 mode is still observed and check its position

this is to see the stability and the effect of the temperature.

05 April  2021 :  A rough alignment of the cavity was done using the Helium Neon Laser.

The optical spectrum of the GHz oscillator: FWHM ~ 4nm